What is thelaziosis?

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Most pet owners probably don’t associate the scientific name “thelaziosis” with the eyeworm infestations their dogs experience. However, the so-called eyeworm Thelazia callipaeda is an emerging parasite that spreads across Europe. Effective prevention is essential to keeping pets, and humans, healthy.

It is a disease caused by a worm. Actually, an infection by a small white worm called Thelazia callipaeda that lives on the surface of the eyes – usually under the third eyelid – of domestic and wild carnivores such as dogs, cats, foxes, as well as other mammals, such as rabbits. This eyeworm causes conjunctivitis and keratitis (inflammation of the cornea). Corneal ulcers, perforation and blindness can also present in different and serious ways.

Parasites are transmitted from one animal to another, including man, through various species of flies, which can act as intermediate hosts.

The most common ocular signs seen in infested dogs include conjunctivitis, epiphora (excessive tearing), itching, purulent discharge, and blepharospasm (involuntary closing of the eyes).

For decades, the distribution of these eyeworms had been limited to Asia and the former Soviet Union. However, the parasite is spreading throughout the European continent due to infected dogs traveling to / from endemic regions.

The main clinical signs in both animals and humans are excessive tearing, conjunctivitis, and inflammation of the cornea. Eye itching can also be a warning sign. In severe forms, corneal ulcers, perforation, and blindness can also occur. Any sign of eye irritation should raise clinical suspicion. Diagnosis and treatment should be done by your veterinarian. It consists of the mechanical elimination of the worms with a swab and / or by washing the conjunctival sac of the eyes. A pharmaceutical treatment can be added.

In Spain the first cases were found in the north of Extremadura (Vera region, Cáceres) and at present Cáceres and Orense are endemic areas. Autochthonous cases have been detected in the Sierra de Guadarrama (Madrid and Segovia), Granada, León and Lleida, their usual habitat being areas of oak forests.

The prognosis of canine ocular Thelaziosis is excellent, as long as all worms are eliminated and there are no complications such as deep ulcers.

If in doubt, go to your vet.

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